Some of the second colour-option are VERY hard to tell from another. 
  
I just played a Smoke vs Smoke match where both he and I selected the second costume. 
... That was one confusing match! 
To my favour apparently (since I won), but really... I lost track of my guy several times during the match.
It was kind of amusing though. 

Apart from the colours of the characters being similar... all the teleporting and smoke-trails are sure to cause confusion :-)

Jade vs Jade for the klassic costume is impossible to tell apart lol

Noob vs Noob is pretty bad too.

I remember watching a scorpion vs scorpion match a while back where they where slightly different tones of yellow, very confusing especially if you arent playing

Jade vs Jade for the klassic costume is impossible to tell apart lol

@xhavoc86 said:

Jade vs Jade for the klassic costume is impossible to tell apart lol

Hell yes!

i don't get this,  in the past they were palette swaps so changing colors would mean completly diferent character but now it makes no sense and some characters have very different colors like liu kang he has red default and blue alt i've been complaining about this in the mk forums for a while now i hope they fix it with a patch